Example embodiments of the invention relate to ink compositions, methods of preparing ink compositions and display panels including ink compositions. More particularly, example embodiments of the invention relate to electronic ink compositions used for reflective type display panels, methods of preparing the electronic ink compositions, and display panels including the electronic ink compositions.
A reflective type display device may display an image utilizing an external light without a light source while a liquid crystal display (LCD) device or a plasma display panel (PDP) device has an internal light source such as a back light. The reflective type display device uses the external light so that the reflective type display device may ensure low power consumption. Additionally, the reflective type display device may have a very thin thickness because the reflective type display device does not include the light source. However, the reflective type display device does not properly display various color images so that the reflective type display device has not been widely employed in various electric and electronic apparatuses.
In such circumstances, Amazon has succeeded in developing Amazon Kindle and the reflective type display device attracts much concern again. Amazon employed the reflective type display device in an e-book, Kindle. While using the e-book, power may be consumed only when changing screens and the power may not be consumed while reading a book. In addition, the e-book may have a merit of making eyes comfortable after reading for a long time like a paper. The Kindle was highly acclaimed on the market. Further, as the appearance of iPad visualizing a supply of diverse contents, possibilities on replacing the paper with a display device has attracted much attention.
The reflective type display device may be applied as a newspaper, a recyclable paper display device for a cellular phone, a portable TV screen and an electronic wall paper by using an electronic ink or an E-ink and by being manufactured through a known method. The technique on the electronic ink includes a particle-based electrophoresis display device, in which a plurality of charged particles moves here and there in a suspension liquid under an influence of an electric field.
Here, an electrophoresis phenomenon means a moving phenomenon of charged particles with an application of an electric field. When electrophoresis is generated in a liquid, the charged particles may move at a velocity determined by viscous drag, a charge, dielectric properties of the liquid, and a magnitude of applied electric field.
In an electrophoresis display device, a color may be determined by using particles having one or more colors dispersed in a dielectric liquid of different color. That is, when an electric field is applied to the particles having one or more colors, the charged particles may move to an electrode having an opposite sign with respect to the electric field. As the result, color change may be observed in visual.
The electrophoresis display device may have a good luminance and contrast, a wide viewing angle, a state bistability and low power consumption when compared to an LCD device. However, problems concerning an image quality deterioration of the display device after a long time has been disturbed the propagation of the electrophoresis display device. Particularly, the particles constituting the electrophoresis display device may have a precipitating tendency and so, a service life of the electrophoresis display device may become insufficient. In order to solve the problems, properties on a high contrast ratio, a rapid response time, and bistability may be required to be confirmed for the particles used in the electronic ink.
International Patent Publication No. PCT/WO2005/036129, and U.S. Pat. Nos. 5,961,804 and 5,930,026, to E-ink Cooperation in U.S.A., disclose a reflective type electronic ink having the above-described properties. A core-shell coating was performed on the surface portion of pigment particles through an acryl initiation reaction using lauryl acrylate having a good compatibility with a low dielectric liquid, and at least one non-compatible monomer selected from the group consisting of styrene, t-butyl methacrylate, N-vinyl pyrrolidone acrylic acid, acrylonitrile, methyl vinyl ketone and methacrylamide. However, since acryl monomers used to impart a charge may have a low polarity and may not overcome a driving velocity to achieve videos, an ionic type functionality having a high polarity may be required to be introduced.
In accordance with the above-described publications, an electronic ink having a particle dispersed liquid phase was obtained by using the core-shell coated particles along with a low dielectric liquid and a charge control agent (CCA). And a method of sealing the electronic ink into micro capsules is disclosed.
However, reflective type display devices manufactured by the above-described methods have lots of defects. Particularly, an electrophoresis display device including the micro capsules may be too sensitive to environmental changes (particularly, to humidity and temperature) because of the wall of the micro capsules. In addition, the electrophoresis display device including the micro capsules may have a weak scratch resistance because of the thin wall of the micro capsules and a large particle size.
In order to improve handling on the display device, the micro capsules may be required to be buried in a large amount of a polymer matrix. In this case, the distance between two electrodes may get farther and a response time may be slowed. In addition, the small loading amount of pigment particles may lower the contrast ratio.
While performing an encapsulation process, CCAs may diffuse to an interface of water/oil and an increase of a surface charge density on the pigment particles may become difficult. The low charge density or zeta potential of the pigment particles in the micro capsules may retard the response time. In addition, since the particle size of the micro capsules may be large and the distribution range thereof may be wide, an electrophoresis display device of this type may exhibit a worse dissolution and addressability while applying color. Therefore, a method of injecting a reflective type electronic ink by the method introducing the micro capsules may not be applied, but a method of injecting an ink into micro walls may be designed.
In accordance with the above-described common methods, the particles for the electronic paper of the display device may be obtained by applying the core-shell coating process using an acrylate monomer and by an initiation polymerization to impart a charge for an electrophoresis and to obtain dispersion stability. The particles may be sealed in a capsule by mixing with a low dielectric liquid. However, various problems including defects accompanied by the manufacturing process as described above and a defect of difficulty in dispersion into a low dielectric liquid may remain.